Prolonged Exposure to Elevated Iodine Levels in Drinking Water Is Associated With the Occurrence of Autoimmune Thyroid Disorders in Adults: Findings From a Case-Control Study Conducted in Shandong Province, China.

Excessive iodine intake is associated with an increased risk of thyroid autoimmunity. However, the relationship between prolonged exposure to iodine levels exceeding 100 μg/L in drinking water and the occurrence of autoimmune thyroid disorders (AITDs) remains uncertain. The objective of the present study was to assess whether elevated iodine levels exceeding 100 μg/L in drinking water are a risk factor for AITD. We conducted a case-control study at a hospital, enrolling 668 adults. We measured serum thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), urinary iodine concentration (UIC), water iodine concentration (WIC), and serum cytokine concentrations-including interleukin-1β (IL-1β), interleukin-6 (IL-6), interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α). The study demonstrated that individuals with water iodine levels > 100 μg/L had a significantly higher risk of developing AITD compared with those in the 10-100 μg/L group (OR = 2.076, < 0.001). Furthermore, a family history of thyroid disorders (OR = 4.035, < 0.001) and higher education levels (specifically college education compared to primary school; OR = 2.608, =0.016) were associated with an increased risk of AITD. Conversely, regular consumption of freshwater fish was correlated with a lower risk of developing AITD (at least once per week vs. hardly eat, OR = 0.472, =0.009; at least once per month vs. hardly eat, OR = 0.693, =0.042). Additionally, IL-6 levels in the case group were significantly higher than those in the control group. The case-control study demonstrated a significant association between the development of AITD and prolonged exposure to elevated iodine levels (above 100 μg/L) in water. AITD was found to be associated with several other factors. Risk factors for AITD include a family history of thyroid disorders and higher educational attainment. Additionally, the consumption of freshwater fish was identified as a protective factor. Identifying and understanding these significant risk and protective factors for AITD development are critical, and effective strategies should be developed and implemented for prevention and intervention targeting at-risk individuals.